It is known, as described in Japanese Patent Application (OPI) No. 90296/79 (the term "OPI" as used herein means a "published unexamined Japanese patent application"), that thermoplastic aromatic polyether ketone resins are superior in heat resistance, flame resistance, mechanical and electrical properties, and chemical resistance. Because of these superior properties, it has been suggested to utilize the resin particularly in electrically insulating coating of electrical wires and cables. But the use of the resin is not limited to the coating of electrical wires or cables. That is, a further development is expected in various industries in the electrical or mechanical field by expanding its range for use by means of imparting electrically insulative coating, anti-corrosion property, etc. to various electrically conductive materials.
In order to impart excellent properties of such thermoplastic aromatic polyether ketone resins such as electrical insulation and anti-corrosion properties to metal substrates, especially steel, aluminum and copper, extensive investigations on the coating of the thermoplastic aromatic polyether ketone resin have been made by the present inventors. As the results, there were previously proposed the following procedures for forming a good coating film: a method in which a polyether ketone having a specific particle diameter is applied onto the surface of a substrate, melted at a specific temperature, and then cooled to form a strong coating film (see Japanese Patent Application (OPI) Nos. 127768/83 and 130574/84; and a method in which a molten polyether ketone is fused onto the surface of a substrate and then cooled to form a strong coating film (see Japanese Patent Application No. 83289/83).
The polyether ketone coating films obtained by the above methods retain the superior properties of the polyether ketone resin, i.e., high heat resistance, flame resistance, mechanical and electrical properties, chemical resistance, and resistance to boiling water, and further can impart high electrical insulation, corrosion resistance, and resistance to boiling water to the metal substrate, whereby they are proceeding development of useful products and are contributing to development of the industry.
The polyether ketone resin does not undergo chemical deterioration even when exposed to boiling water or steam of more than 200.degree. C. Because of such superior resistance to boiling water and resistance to steam, the polyether ketone resin is expected to be used in various fields, e.g., nuclear power field, oil drilling field, etc. as well as various chemical equipments. The polyether ketone resin, however, is poor in water repellancy (a property to repel water). When it is, for example, applied to a level gage of boiling water, there are caused various problems such as an error in the detection of the boiling water dip surface and easy occurrence of scale. Thus it has been strongly desired to improve the water repellency in many applications using boiling water.
As a result of extensive investigations, it has been found that a composition as described below can produce a coating film which is improved in water repellency without deteriorating the superior properties of the polyether ketone resin, such as resistance to boiling water and resistance to steam, exhibits good adhesion to a substrate, has good appearance, and further is free from pinholes, leading to accomplishment of the present invention.